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New glass etched with nanograss structures can be switched from hazy to clear by applying water. As shown here, removing the water from the glass makes it appear hazy again. This switchable glass could offer a simple and inexpensive way to make smart windows that change between clear and opaque. Credit Sajad Haghanifar, University of Pittsburgh

A new glass could improve the performance of solar cells and LEDs.

A research team from the University of Pittsburgh has developed glass that can let through substantial amounts of light while appearing hazy, marking the first time that glass has been made with such high levels of haze and light transmittance at the same time.

“Switchable glass available today is quite expensive because it uses transparent conducting layers to apply a voltage across the entire glass,” Paul Leu of he University of Pittsburgh's Swanson School of Engineering, leader of the research team, said in a statement. “Our glass would be potentially less expensive to make because its opacity can be switched in a matter of seconds by simply applying or removing liquid.”

The glass, which is already being touted as a boost to the performance of solar cells and LEDs, can be switched from hazy to clear by simply applying water, making it useful for smart windows that change haze or opacity to control the privacy of a room or to block glare from sunlight.

“The water goes between the extremely hydrophilic nanostructures, making the nanograss glass act like a flat substrate,” graduate student Sajad Haghanifar, the project’s lead, said in a statement. “Because water has a very similar index of refraction to the glass, the light goes straight through it.

“When the water is removed, the light hits the scattering nanostructures, making the glass appear hazy,” he added.

The new glass achieves a record 95 percent light transmittance and a similarly high degree of haze at the same time.

The researchers experimented with glass etched with nanograss structures from 0.8 to 8.5 microns in height with "blades" each measuring a few hundred nanometers in diameter.

The new glass uses a pattern of nanostructures that is similar to grass that increases the likelihood that light will be scattered and could potentially increase the amount of light that makes it from a semiconductor into the surroundings.

The researchers found that shorter nanograss improved the antireflection properties of the glass while longer nanograss tended to increase the haze. Glass with 4.5-micron-high nanograss showed a balance of 95.6 percent transmittance and 96.2 percent haze for light with a 550-nanometer wavelength.

To turn the glass into a smart window that switches from hazy to clear, it would require placing a piece of traditional glass over the nanograss glass, while pumps could be used to flow liquid into the space between the two glasses, and a fan or pump could be used to remove the water.

“We are now conducting durability tests on the new nanograss glass and are evaluating its self-cleaning properties,” Haghanifar said. “Self-cleaning glass is very useful because it prevents the need for robotic or manual removal of dust and debris that would reduce the efficiency of solar panels, whether the panels are on your house or on a Mars rover.” 

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